Drug Class

Second-generation antihistamine
(Peripheral H1 receptor blocker – non-sedating)

H1 receptors are present in:

Brain → Sedation (minimal effect )
Skin → Itching, urticaria
Lungs → Allergic responses
Nose → Sneezing, rhinorrhea
Blood vessels → Vasodilation, edema

Peripheral H1 receptors are present in

Lungs → Allergy symptoms
Skin
Nose
Blood vessels

Central H1 receptors are present in

Brain
⚠️ Loratadine has minimal penetration into the brain, so sedation is very low.

Brand Names

India:

Lorin, Lariago-L (combo), Claritin (imported)

USA

Claritin

UK / Europe:

Clarityn, Claritin

Approved By

• FDA (United States)
• CDSCO (India)
• EMA (Europe)

Available Strengths & Dosage Forms

• Tablet: 10 mg
• Syrup: 5 mg / 5 ml (paediatric use)
• ODT (orally disintegrating tablet): 10 mg

Purpose / Indications

Loratadine is used to treat allergic rhinitis and chronic urticaria by blocking peripheral H1 receptors without causing significant sedation.

Symptoms It May Cure

• Sneezing
• Runny nose
• Itching (nose, throat, skin)
• Watery eyes
• Urticaria (hives)
• Allergic skin rash
• Seasonal allergies (hay fever)

Dosage

Adults

10 mg once daily (OD)

Children

2–5 years: 5 mg once daily
≥6 years: 10 mg once daily

⚠️ Dose adjustment required in severe liver impairment.

Mechanism of Action of Loratadine

Loratadine selectively blocks peripheral H1 histamine receptors.

• Prevents histamine from binding to H1 receptors
• Reduces vasodilation
• Decreases capillary permeability
• Controls itching and mucus secretion

Unlike first-generation antihistamines:

• Causes minimal sedation
• It does NOT significantly cross the blood–brain barrier

Detailed Explanation

During an allergic reaction:

• Mast cells release histamine
• Histamine binds to H1 receptors
• Causes itching, redness, swelling, sneezing

Loratadine blocks H1 receptors → prevents these symptoms.

It is metabolized in the liver to desloratadine (active metabolite).

Bioavailability

Definition:

Bioavailability refers to the percentage of a drug that reaches systemic circulation in an active form after administration.

Bioavailability:

Approximately 40% (due to first-pass metabolism).

Food may slightly delay absorption but does not significantly affect overall effect.

Half-Life

Definition:

Half-life is the time required for the plasma concentration of a drug to reduce to half of its original value.

Half-Life:

Parent drug: ~8 hours
Active metabolite (Desloratadine): ~27 hours

This is why it is given once daily.

Summary Statement

Loratadine is a second-generation peripheral H1 blocker that effectively controls allergic symptoms such as sneezing, itching, and urticaria with minimal sedation, making it suitable for daytime use.

Additional Pharmacological Points

• Does NOT significantly cross BBB
• Minimal sedation
• No significant anticholinergic activity
• Metabolized by CYP3A4 & CYP2D6
• Active metabolite: Desloratadine

Side Effects

Common Side Effects

Headache
Dry mouth
Fatigue (rare)
Nausea

Less Common / Rare

Palpitations
Liver enzyme elevation (rare)

Contraindications

• Severe hepatic impairment (dose adjustment required)

Dosage Frequency

Once daily (OD)
Suitable for daytime use

Use in Special Populations

Pregnancy

• Previously Category B (old classification)
• No proven teratogenic risk
• Generally considered safe
• Use only if clinically needed

Lactation

• Passes into breast milk in small amounts
• Usually considered compatible with breastfeeding

Elderly

• Generally safe
• Monitor in liver impairment

Drug Interactions

• CYP3A4 inhibitors (ketoconazole, erythromycin)
• Cimetidine
• Other antihistamines

Storage Instructions

• Store at room temperature
• Protect from moisture
• Keep out of reach of children

Disclaimer

This information is for educational purposes only and should not replace professional medical advice. Always consult a doctor before using any medication.

Extras

It is preferred for:
✔️ Daytime allergy relief
✔️ Long-term allergic rhinitis
✔️ Chronic urticaria

Not ideal for:
Acute severe allergic reactions (not a substitute for epinephrine)

Key points / Revision

Point	Details
Drug Class	Second-generation antihistamine
Receptor Blocked	Peripheral H1
Blood–Brain Barrier	❌ Minimal crossing
Sedation	Low
Generation	Second
Main Uses	Allergic rhinitis, urticaria
Active Metabolite	Desloratadine
Bioavailability	~40%
Half-life	8 hrs (parent), 27 hrs (metabolite)
Pregnancy	Generally safe
Lactation	Usually compatible
Best For	Daytime allergy
Not Ideal For	Severe anaphylaxis